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Estimating the Potential Impact of Emerald Ash Borer (Coleoptera:
Buprestidae) Presence in the DePauw University Nature Park
Megan Walton, Neil Broshears, Alex Eades, and Amanda Hendricks
DePauw University – Greencastle, IN
ABSTRACT Emerald Ash Borer (Coleoptera: Buprestidae) is an invasive beetle that is native to Asia. It is
assumed that it arrived in 2002 in the Michigan harbor areas via wooden shipping crates (Haack et al. 2002). The
Emerald Ash Borer (EAB) feeds on the phloem of ash tree species (Fraxinus spp.) native to the Northeastern United
States and lays its larvae underneath the bark. This activity cuts off the water supply to the tree and leads to the
eventual death of the host (Purdue Extension 2008). This poses a large threat to the ecosystem and economy of the
areas affected (MacFarlane and Meyer 2005). We investigated whether or not EAB has arrived in Putnam County,
more specifically the DePauw Nature Park and Arboretum. EAB was not found in our study area. Through
observational field studies, GIS mapping and analysis we predicted the potential impact of EAB introduction to the
ash tree population in the Arboretum and Quarry South. Since we found that ash trees comprise less than 1% of the
forest structure, we conclude that EAB invasion would not have a detrimental effect on the Arboretum and Quarry
South forest composition.
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Introduction
Emerald Ash Borer (Coleoptera:
Buprestidae) is an invasive beetle pest
whose larvae feed on the phloem of ash trees
(Fraxinus spp.) found in the inner cambium
(Figure 1). This feeding activity leads to a
girdling effect, cutting off the supply of vital
nutrients and water and leading to the
eventual death of the ash tree within 3-5
years after infestation (Poland and
McCullough 2006). Adults can fly in 8-12
meter bursts, allowing it to move from one
tree to another very easily (Haach et al.
2002). As a population, EAB has been
spreading at an approximate rate of 0.6
miles per year (Poland and McCullough
2006). This rate may appear slow but poses
a large threat to forest stands throughout the
Midwest.
The Emerald Ash Borer (EAB) is native
to China, Korea, Mongolia and Japan
(Haach et al. 2005). In 2002, EAB was
identified for the first time in North America
in Detroit, Michigan and Windsor, Ontario
(Poland and McCullough 2006). It is
commonly believed that EAB was
introduced to North America by transfer of
wooden crates and pallets used in shipping
from Asia. Quarantine efforts have been
implemented in all infected counties but due
to a lack of awareness of quarantine
guidelines, EAB has spread to areas in Ohio,
Maryland, Virginia, and Indiana (BenDor et
al. 2006).
The potential impact that EAB could have
on North America is massive in terms of
both biological and economic costs. The
impact depends on the distribution and
overall health of the ash tree populations
Fig. 1. Emerald Ash Borer (Purdue Extension 2008).
in North America. Knowledge of the ash
tree distribution could help identify the
potential risk that North American forests
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face if EAB continues to spread (McFarlane
and Meyer 2005).
The elimination of ash trees by EAB
could potentially have a negative impact on
the ecosystem as well as the economy.
Heavy loss of ash trees within forests could
dramatically alter the biodiversity of the
local ecosystem. In urban areas, where ash
is commonly planted as street trees, dead
trees create a burdensome cost for removal.
The wood of ash trees is commonly used in
the manufacturing of baseball bats,
furniture, cardboard and paper (Poland and
McCullough 2006). The total compensatory
value of ash trees has been estimated to be
as high as $282.3 billion in the United States
alone (Poland and McCullough 2006).
As of 2005, prior to the discovery of EAB
presence in 16 additional counties in Indiana
(Purdue Extension 2008), a total of 48
United States counties had a confirmed
presence of EAB populations (McFarlane
and Meyer 2005) (Figure 2). In 2003, there
were an estimated 7 billion ash trees in the
country. Of these, 150 million or 2 percent
are in Indiana (Liu et al. 2003). Green,
white, and black ash species are the
preferred hosts of EAB, and trees
experiencing greater stress are more
susceptible (Poland and McCullough 2006).
As residents of Indiana and the DePauw
University campus community, we were
interested in whether EAB had spread to
Putnam County. There are three
quarantined counties each within a 75 mile
radius of Putnam County (Purdue Extension
2008). We conducted a survey of the
Arboretum and Quarry South of the DePauw
University Nature Park in Greencastle,
Indiana for the presence of EAB. If the
beetle was found to be present, the correct
authorities would be notified and a plan to
eradicate all infected trees would have been
implemented.
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Additionally, we mapped the potential
impact that EAB would have on older and
younger eastern deciduous forest stands in
the Nature Park if EAB were to reach
Putnam County and the DePauw University
Nature Park. The Nature Park was given to
DePauw University in 2004, and over the
past 35 years since the abandonment of the
quarry, the Arboretum and the areas around
the quarry have been undergoing ecological
succession (DePauw University 2008).
Therefore we chose our site locations to
represent the young and old forest stands of
the Nature Park, Quarry South and the
Arboretum, respectively. Identification of
EAB presence in the Nature Park as well as
its potential impact on our forest could
provide valuable information for prevention
or management strategies on campus as well
as within the Putnam county communities.
We hypothesized that it would be unlikely
for EAB to be present in Putnam County. If
EAB were present, we expect that younger
tree stands will be more affected than older
tree stands. Thus the forest plots located in
the Arboretum may be more affected than
Quarry South. Additionally, the presence of
EAB, and the resulting loss of ash trees will
likely have a large detrimental effect on tree
canopy.
Methods
Study Area and Sampling Design
Methods were modified from the
Breeding Biology Research and Monitoring
Database (BBIRD) developed by Thomas E.
Martin et al. (1997). We restricted our study
to Quarry South and the Arboretum of the
DePauw University Nature Park located in
Greencastle, IN. These locations contain
young (Quarry South) and old (Arboretum)
eastern deciduous forest stands found in the
Nature Park. They also contain an unknown
proportion of ash trees. To examine the
presence of Emerald Ash Borer (EAB) as
well as the proportion of ash trees within
these two areas, five additional plots per site
were sampled and compiled with data
collected by Dr. Vanessa Artman during
2004 and 2006. Dr. Artman’s ecology
students collected data on tree species
composition of 20 plots in each site. The
inclusion of these data enabled us to more
accurately determine the ash composition in
each of the sites.
We chose our sample sites using random
computer-generated numbers for grid point
(location in Nature Park assigned by a grid
system by Dr. Artman), compass direction
and distance from grid points. This location
was assigned as the center of our vegetation
plot and was marked with an orange flag
indicating the site name.
Adult Tree Data Collection
Latitudinal and longitudinal GPS
coordinates were collected at the center of
each plot and recorded using handheld GPS
units. After site location was determined and
recorded, a radius of 11.3 meters was
marked using a tape measure (Figure 3). All
trees within the 11.3 meter radius of the plot
were measured for circumference using a
tape measure. All trees with trunks located
at least half-way inside the circumference of
the sample plot were included. Trees were
placed into one of three size categories
determined by diameter at breast height
(1.38m): small trees (8-23cm), medium trees
(23-38cm) and large trees (>38cm) (Martin
et al.). Trees with a diameter less than 8.0
cm were not considered trees for this study
and were thus not included in the data.
All ash trees identified within the plots
were marked with orange flagging tape as
well as a numbered metal tag at breast
height facing west. The tag number was
recorded in our data. All other tree species
were recorded as “other”. Upon
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identification of ash trees (Purdue Extension
2008), we surveyed the tree trunk from
ground to breast height for the presence of
EAB. Key identifiers included D-shaped
exit holes, vertical splitting of bark,
epicormic shoots forming from latent buds
on the trunk (often a result of severe
defoliation), die-back of leaves and evidence
of unusually high presence of woodpeckers
(Purdue Extension 2008).
Tree height was recorded for all ash trees,
within our plots using a clinometer. To
determine ash tree age, core samples were
collected from the ash tree closest to the
center of the plot using a tree corer. Core
samples were placed into plastic drinking
straws to protect them from breaking and
marked with the ash tree tag number.
These methods were completed during
early spring, prior to leafing-out, to obtain
accurate GPS coordinates and clinometer
readings.
Sapling/Shrub Data Collection
After leafing out occurred, we returned to
our sample vegetation plots and recorded the
number of tree saplings and shrubs located
within a 5 meter radius of the center of each
plot (Figure 3). Only saplings and shrubs at
breast height or taller were included. We
also counted the number of ash tree saplings
within this 5 meter radius. Identification of
ash tree saplings was done by leaf
identification. We double-checked our
identification of adult ash trees using leaf
characteristics to ensure that our previously
collected data were accurate.
Core Sample Age Identification
All ash tree core samples were sanded
using 220 and 320 grit sandpaper until
individual rings were visible to the naked
eye. Linseed oil was brushed over the core
sample with gauze to create enough contrast
in color that age could be determined. Rings
were counted using a dissecting microscope.
Due to poor quality of the core samples,
correct age could not be determined and
these data was not included in the study.
Data Compilation and Mapping
Fig. 3. Vegetation plot diagram, modified from the
BBIRD Field Protocol (Martin et al. 2007).
We compiled our data with the 2004-2006
tree data provided by Dr. Vanessa Artman
into a spreadsheet using Microsoft® Excel.
These data were mapped using ArcGIS
software. The maps show ash and non-ash
density and size in both Quarry South and
the Arboretum (Figures 9 & 10). They also
show the location of our sample sites in an
aerial photograph of the Nature Park (Figure
4).
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and ecology. An invasive pest can
considerably change the ecological
composition of the environment in which it
is introduced. In the case of EAB, its
introduction could drastically impact the tree
canopy and thus ultimately alter the flora
and fauna of the forest floor. Fragmentation
of forest habitat could occur in extreme
cases of EAB outbreak. Conservation
strategies, such as quarantines and
eradication of infected trees are important
actions to take to protect the forests of the
Midwest. The data that we collect on ash
composition in the DePauw Nature Park
could help us identify risk as well as create
prevention and management protocols. Our
data and analysis are relevant to the goals
and ethical principles of conservation
biology in that our efforts could lead to
greater awareness of the potential risks that
the forest stands of DePauw University face.
If we had found EAB in our study sites, we
could have played an immense role in
protecting the biological community.
Fig. 4. GIS map of our plot locations (yellow) in
addition to Dr. Artman’s plot locations (blue) in the
Arboretum (upper right) and Quarry South (lower
left).
Results
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Data Analysis
Data were analyzed using a one-way
ANOVA to determine if differences existed
between Quarry South and Arboretum ash
tree densities and size, average number of
trees per plot, and forest structure (tree size).
Additional one-way ANOVA tests were run
to compare densities of ash tree saplings
between the two sampling areas.
Number of Trees
30
25
20
15
10
5
0
Arboretum
Quarry South
Site
Fig. 5. Average number of trees per plot in the
Arboretum versus Quarry South.
Relevance to Conservation Biology
This study pertains to conservation
biology because it is an observational study
of the potential impact of an invasive
species on a forest community’s biodiversity
As shown in Figure 5, the Arboretum had
an average of 21.88 trees per plot, whereas
Quarry South had an average of 28.92 trees
per plot. There was a significantly greater
number of trees per plot in Quarry South
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than in the Arboretum (F1,48 = 7.841,
p=0.007).
Number of Saplings/Shrubs
3000
2457
2500
2000
1755
1500
Arboretum
1000
500
Quarry South
201
153
0
Ash
Non-Ash
Site
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Number Trees
30
25
Small
20
Medium
15
Large
10
Fig. 8. Number of ash versus non-ash saplings and
shrubs in the Arboretum versus Quarry South.
5
0
Arboretum
Site
Quarry South
Fig. 6. Comparison of forest structure between the
Arboretum and Quarry South.
The number of large trees in the
Arboretum was significantly higher than in
Quarry South (F1,48=9.164, p = 0.004). The
number of medium and small trees was
significantly higher in Quarry South than in
the Arboretum. (F1,48=7.010, p = .011;
F1,48=8.954, p = 0.004, respectively) (Figure
6).
1.6
1.4
Number Trees
1.2
1
Small
0.8
Medium
0.6
Large
0.4
0.2
0
Arboretum
Site
Quarry South
Fig. 7. Number of ash trees of each size category in
the Arboretum versus Quarry South.
The number of ash trees did not differ
between the Arboretum and Quarry South
(F1,48 = 0.637, p=0.429, Figure 7).
Non-ash saplings and shrubs were
significantly more abundant than ash
saplings in both the Arboretum and Quarry
South (χ2<0.001, df=1). For every ash
sapling in a Quarry South plot, there were
16.1 non-ash saplings and shrubs. And for
every ash sapling in the Arboretum, there
were 8.7 non-ash saplings and shrubs.
There was a greater proportion of ash
saplings in the Arboretum than in Quarry
South.
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Fig. 9. GIS map of ash and non-ash tree density and
size in the Arboretum.
As shown in Figure 9, ash trees comprised
a small proportion of the total trees in the
Arboretum. Most of the ash trees were in
the medium and large size categories. Nonash trees, comprising the majority of the
Arboretum forest site, were primarily found
in the small size category.
As shown in the map, there were
three separate clusters of ash trees in the
Arboretum. One is found at the
northernmost region of the site, another in
the west-central region, and another at the
southernmost region.
Fig. 10. GIS map of ash and non-ash tree density and
size in Quarry South.
As shown in Figure 10, there was a higher
proportion of small non-ash trees in Quarry
South compared to the Arboretum.
Additionally, very few ash trees are located
in Quarry South compared to the
Arboretum. Small non-ash trees were
predominant in Quarry South. Most of the
ash trees in Quarry South are located in a
cluster in the east-central region of the site.
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Discussion
Our results show that Quarry South has,
on average, more trees per plot than the
Arboretum (Figure5) and that the trees
found in the Arboretum are typically larger
than those found in Quarry South (Figure 6).
This makes sense given that the Arboretum
is the older forest site. Thus an older site
will likely contain fewer young trees
because its canopy is further developed and
older trees are already established.
Our results suggest that the estimated
threat to Quarry South and the Arboretum is
relatively minimal given that each site
contains less than 1% ash.
There was a significantly higher
proportion of ash saplings per plot in the
Arboretum than in Quarry South (Figure 8).
This may be due to the presence of better
quality soil for ecological succession in the
Arboretum, given that it has gone
undisturbed by humans much longer than
Quarry South, which was left as an
abandoned quarry site 35 years ago
(DePauw University 2008).
The trend of finding ash trees in small
clusters as shown in the GIS maps (Figure 9
& 10) can be explained by soil type or slope
of the land. In locations where past human
activity included logging, particularly in
Quarry South, the forest at one point may
have been fragmented and resulted in a
clustered distributions of trees in areas such
as slopes that were too steep to log. The
Arboretum would likely have better quality
soil as well due to its older age in
comparison to Quarry South, and may be the
reason that it has three main clusters of ash
trees, whereas Quarry South only has one. It
would have been beneficial to perform this
study in three different forest sites instead of
two in order to make more conclusive
hypotheses for the reasons behind this
cluster effect.
If we performed this study again, we
would have checked all sites provided by
Dr. Artman for the presence of EAB, rather
than just checking our own. This would
have provided a more accurate means of
determining if EAB had reached Putnam
County. Additionally, we should search for
EAB presence again during late summer
because the larvae emerge as adult borers
beginning in late April and continuing
through the remainder of the summer
(Purdue Extension 2008). Thus, it is likely
that when we made our observations in late
April and early May that we could have
missed the signs of EAB presence.
We also suggest that future studies
include data collection in residential areas in
addition to forests. Ash trees appear to
comprise a greater proportion of tree canopy
in residential areas than in forests. In a
formal letter to the residents of Marion
County, Indiana in 2006 the Marion County
Tree Board declared that ash trees comprise
14% of Indianapolis’ residential tree canopy
(Holdsworth 2006). Thus, introduction of
EAB would likely have the most detrimental
impact in residential areas than it would in
forest sites.
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